JP3947748B2 - Optical amplifier with quantum dots - Google Patents

Description

  The present invention relates to an optical amplifier using quantum dots, which is particularly applied to fields such as nanoscale optical communication networks and optical measurement.

  With the recent development of semiconductor microfabrication technology, a semiconductor element having a fine structure up to a size at which a quantum mechanical effect appears noticeably has been realized (for example, see Non-Patent Document 1). As semiconductor elements utilizing this quantum mechanical effect, for example, HBT (Hetero-junction Bipolar Transistor) and quantum well lasers have been put into practical use. In addition, nanoscale quantum dots that take advantage of the particle properties of electrons by controlling single electrons using quantum mechanical effects have attracted attention.

  Quantum dots are formed by using the above-described semiconductor microfabrication technology to form a box with a potential that is so fine that it gives three-dimensional quantum confinement to excitons. Utilizing this exciton confinement system, the energy levels of carriers in the quantum dot become discrete, and the density of states sharpens in a delta function. Single-electron memories that use light absorption between the sharpened states of this quantum dot and single-electron transistors that turn on / off single electrons that enter and exit the quantum dot have already been studied. Nanoscale manipulation is being realized.

M. Ohtsu, K. Kobayashi, T. Kawazoe, S. Sangu, T. Yatsui, IEEE J. Sel. Top. Quant. Electron., To be published Vol8.No4 2002 July-Aug, P839-P862

  By the way, in order to meet the demand for future large-capacity information processing, it is desired to realize a nanoscale optical amplifier capable of performing optical amplification without being controlled by the diffraction limit of light.

  However, when trying to realize such a nanoscale circuit with an electronic device, problems such as power consumption and heat generation occur, and when trying to realize it with an optical device, miniaturization is still limited by the diffraction limit of light. There is a problem of being done. In addition, an amplifier is necessary because the signal in the nanoscale element is small, but there is no practical optical amplifier that can operate at the nanoscale. Furthermore, when trying to realize this with a quantum device, there is a problem that an apparatus for ensuring coherence for a long time becomes large. For this reason, a practical nanoscale optical amplifier itself has not yet been devised.

  Therefore, the present invention has been devised in view of the above-described problems, and finds a unique photophysical phenomenon between quantum dots arranged in the nanometer region, and allows light to be controlled without being controlled by the light diffraction limit. An object of the present invention is to provide an optical amplifier using quantum dots capable of performing amplification processing and the like on a nanoscale.

  In order to solve the above-described problems, an optical amplifier using quantum dots according to the present invention includes a dielectric substrate and an excitation state in which excitons are excited according to input light that is formed on the substrate and supplied from the outside. A first quantum dot having a position, and two second quantum dots formed on a substrate so as to sandwich the first quantum dot and having a larger volume than the first quantum dot, Each of the second quantum dots has substantially the same resonance energy level in which excitons are excited based on induced light supplied from the outside, and input light supplied to the first quantum dots. Based on the above, output light is generated by amplifying it.

  In the optical amplifier using quantum dots according to the present invention, the first quantum dot having the excitation level excited by the exciton according to the input light supplied from the outside and the first quantum dot are sandwiched between the first quantum dot and the first quantum dot. Two second quantum dots each having a large volume are formed on a substrate, and each second quantum dot has substantially the same level in which excitons are excited based on induced light supplied from the outside. Resonance energy level. When input light is supplied to the first quantum dot of the optical amplifier having such a configuration, the state of the excitons excited to the excitation level changes, and this is caused between the second quantum dots. It is possible to break the balance of the nutation phenomenon, and to generate output light according to the strength of the dipole-dipole interaction. In particular, by configuring the second quantum dot with a larger volume, the dipole-dipole interaction can be further increased, so that the light intensity of the output light can be increased and the amplification factor is improved. It becomes possible.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

The present invention is applied to a nano optical amplifier 1 as shown in FIG. The nano optical amplifier 1 is a device that generates output light obtained by amplifying supplied input light on a nano scale. For example, the substrate 10 is made of a dielectric material such as NaCl, KCl, or CaF _2, and the substrate 10 A single first quantum dot 11 formed on the surface of the first quantum dot 11 is formed on the substrate 10 so as to sandwich the first quantum dot 11, and has a larger volume than the first quantum dot 11. Are emitted from the second quantum dots 12a and 12b, the second quantum dots 12a and 12b, and the reflecting mirrors 13a and 13b formed so as to sandwich the second quantum dots 12a and 12b. And an optical antenna 14 for collecting the output light to be output to the outside.

  The first quantum dots 11 and the second quantum dots 12 control single electrons (excitons) based on discrete energy levels formed by confining excitons three-dimensionally. In these quantum dots 11 and 12, the energy levels of carriers are made discrete by the exciton confinement system, and the state density can be sharpened in a delta function.

  The first quantum dots 11 are supplied with input light from the outside. This input light may be supplied to the first quantum dots 11 via a plasmon waveguide (not shown), or may be supplied via a near-field optical probe.

  The second quantum dots 12a and 12b have resonance energy levels whose state density functions are substantially equal to each other, in which excitons are excited based on induced light supplied from the outside. For this reason, the second quantum dots 12a and 12b are made of the same material and have the same volume.

  Each quantum dot 11 and 12 consists of material systems, such as CuCl, GaN, or ZnO. Incidentally, when the material system constituting each quantum dot 11, 12 is CuCl, these are constituted in a cubic shape called a quantum box, and the material system constituting each quantum dot 11, 12 is GaN or ZnO. In some cases, these are configured as spherical or disk-shaped.

  These quantum dots 11 and 12 can be formed on the substrate 10 by using the following Bridgman method. In the case of using the above-mentioned CuCl as a material system constituting each quantum dot 11, 12, CuCl powder and NaCl powder are first mixed and melted at a temperature of about 800 ° C. Next, the molten powder mixture is suspended in a furnace having a temperature gradient in the vertical direction, and moved up and down in the furnace at a speed of several mm / h to create a temperature gradient in the mixed powder gradually. To crystallize. When heat treatment is performed at a temperature of about 200 ° C. for several minutes to several tens of minutes, a NaCl crystal including CuCl quantum dots 11 and 12 can be produced. Incidentally, in this Bridgman method, the size of the generated quantum dots 11 and 12 can be freely controlled by changing the heat treatment temperature and the heat treatment time, and these can be formed side by side in a region of 100 nm or less. Become.

  Each of these quantum dots 11 and 12 may be further formed on the substrate 10 based on a molecular epitaxy (MBE) growth method, and the formation position of the quantum dots with high accuracy using near-field light CVD. You may control.

The quantum confinement level E ( _nx , _ny , _nz ) in each quantum dot 11,12 is expressed by the following formula (1) when the mass of the particle is m and the side length of the quantum dot is L. Defined by
E (n _x , n _y , n _z ) = h ² / 8π ² m (π / L) ² (n _x ² + _ny ² + n _z ² ) (1)
The reflecting mirrors 13a and 13b are provided so as to be parallel to each other so that light incident from the outside (hereinafter referred to as induced light) is reflected back and forth on the second quantum dots 12a and 12b. The reflecting mirror 13a receives induced light having a wavelength λ ₁ from a light source (not shown). For this reason, the reflectance of the reflecting mirror 13a is configured to be slightly lower than 100% so that the induced light can be incident from the outside at a constant rate. On the other hand, the reflectance of the reflecting mirror 13b is configured to be approximately 100%. Here, the reflecting mirrors 13a and 13b are provided to increase supply efficiency, but are not necessarily required.

  The optical antenna 14 condenses output light output from both or one of the second quantum dots 12a and 12b and emits the light to the outside. The optical antenna 14 may be composed of, for example, a plasmon waveguide. As an alternative to the optical antenna 14, output light may be picked up using a near-field optical probe.

  Next, the operation of the nano optical amplifier 1 to which the present invention is applied will be described.

  First, input light is supplied to the first quantum dots 11. Here, the first quantum dots 11 are designed so that an excitation level S1 where excitons are excited as shown in FIG. 2 is formed according to the wavelength of the input light supplied. As a result, the state of excitons excited by the excitation level S1 is controlled according to the intensity of the input light supplied to the first quantum dots 11.

Next, the induced light is reflected back and forth between the reflecting mirrors 13a and 13b. Here, the second quantum dot 11 is designed so that an excitation level S2 in which excitons are excited is formed as shown in FIG. 2 according to the wavelength λ ₁ of the induced light that is reflected back and forth. . As a result, excitons are excited in the second quantum dots 12a and 12b in response to the induced light.

  In such a case, excitons go back and forth between the resonating second quantum dots 12a and 12b, so-called nutation is repeated, and this appears in the form of population vibration.

  Incidentally, while this nutation is repeated, a dipole-dipole interaction occurs between the second quantum dots 12a and 12b. During such interaction, the dipoles will be held in anti-symmetric relation to each other.

  When input light is supplied to the first quantum dots 12 as described above when such a nutation phenomenon occurs, the state of excitons excited to the excitation level S1 changes accordingly, and the excitation is further increased. As the state of the exciton at level S1 changes, the balance of the nutation phenomenon is lost. This is because near-field light interaction occurs between the first quantum dots 11 and the second quantum dots 12 with the supply of the input light. As shown in FIG. It means that the direction changes.

  When the orientation direction of the dipole is changed, the output light corresponding to the intensity of the dipole-dipole interaction is emitted from the second quantum dots 12a and 12b, and this is emitted to the outside via the optical antenna 14. become. In other words, the light intensity of the output light is governed by the size of the dipole, and the size of the dipole is based on the size of the quantum dot volume. For this reason, in order to increase the light intensity of the output light, the dipole can be increased by increasing the volume of the second quantum dots 12a and 12b. As a result, the light intensity of the output light emitted can be increased.

  For this reason, the second quantum dots 12a and 12b are configured to have a larger volume than the first quantum dots 11, so that the output light emitted from the second quantum dots 12a and 12b has the first quantum dots. It is possible to control the input light supplied to the dots 11 so as to have an amplified form. In the present embodiment, it is assumed that the size of the first quantum dot 11 is 2 to 3 nm and the size of the second quantum dot 12 is 10 nm. However, the present invention is limited to this case. Instead, the second quantum dots 12 may have any volume as long as the second quantum dots 12 have a larger volume than the first quantum dots 11.

  As described above, the nano optical amplifier 1 to which the present invention is applied finds a unique photophysical phenomenon between quantum dots arranged in the nanometer region, and performs optical amplification processing and the like without being controlled by the diffraction limit of light. Can be done. For this reason, the nano-optical amplifier 1 to which the present invention is applied can be applied to a nano-photonic device that uses a small number of photons as signal carriers, and optical amplification can be performed in nano-order. .

It is a figure for demonstrating per structure of the nano optical amplifier to which this invention is applied. It is a figure for demonstrating about operation | movement of the nano optical amplifier to which this invention is applied.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Nano optical amplifier, 10 Substrate, 11 1st quantum dot, 12 2nd quantum dot, 13 Reflecting mirror, 14 Optical antenna

Claims (3)

A dielectric substrate;
A first quantum dot formed on the substrate and having an excitation level excited by excitons according to input light supplied from the outside;
Two second quantum dots formed on the substrate so as to sandwich the first quantum dots, and having a larger volume than the first quantum dots,
Each of the second quantum dots has substantially the same resonance energy level in which excitons are excited based on induced light supplied from the outside, and is further supplied to the first quantum dot. An optical amplifier using quantum dots, characterized in that output light is generated by amplifying the light based on input light. Each of the second quantum dots generates the output light by changing the state of excitons that reciprocate between resonance energy levels based on the input light supplied to the first quantum dot. The optical amplifier using quantum dots according to claim 1. Each of the second quantum dots generates the output light by changing a dipole state antisymmetric with each other based on input light supplied to the first quantum dot. An optical amplifier using quantum dots according to claim 1.

Images